In part (a), the person sees the image of their eye 60 cm behind the mirror.

In part (a), the person sees the image of their eye 60 cm behind the mirror. The mirror is then turned around as shown in part (b) of the figure above without changing the distance from the person's eye to the vertex of the mirror, and now the person sees the image of their eye 40 cm behind the mirror. Determine the distance from the person's eye to the vertex of the mirror.